全文获取类型
收费全文 | 50680篇 |
免费 | 7047篇 |
国内免费 | 5768篇 |
专业分类
化学 | 32089篇 |
晶体学 | 917篇 |
力学 | 3223篇 |
综合类 | 398篇 |
数学 | 5429篇 |
物理学 | 21439篇 |
出版年
2024年 | 76篇 |
2023年 | 683篇 |
2022年 | 1174篇 |
2021年 | 1397篇 |
2020年 | 1506篇 |
2019年 | 1591篇 |
2018年 | 1459篇 |
2017年 | 1471篇 |
2016年 | 1991篇 |
2015年 | 2079篇 |
2014年 | 2637篇 |
2013年 | 3577篇 |
2012年 | 4264篇 |
2011年 | 4636篇 |
2010年 | 3411篇 |
2009年 | 3455篇 |
2008年 | 3783篇 |
2007年 | 3296篇 |
2006年 | 3143篇 |
2005年 | 2525篇 |
2004年 | 1991篇 |
2003年 | 1625篇 |
2002年 | 1622篇 |
2001年 | 1812篇 |
2000年 | 1344篇 |
1999年 | 1112篇 |
1998年 | 763篇 |
1997年 | 736篇 |
1996年 | 609篇 |
1995年 | 499篇 |
1994年 | 494篇 |
1993年 | 382篇 |
1992年 | 349篇 |
1991年 | 298篇 |
1990年 | 282篇 |
1989年 | 207篇 |
1988年 | 177篇 |
1987年 | 148篇 |
1986年 | 141篇 |
1985年 | 124篇 |
1984年 | 81篇 |
1983年 | 65篇 |
1982年 | 40篇 |
1981年 | 42篇 |
1980年 | 26篇 |
1979年 | 35篇 |
1977年 | 29篇 |
1976年 | 32篇 |
1975年 | 33篇 |
1974年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The oxides A(Ti0.5Te1.5)O6 (A = K, Rb, Cs, Tl), A(Ti0.5W1.5)O6 (A = Rb, Cs, Tl), and Cs(B0.5W1.5)O6 (B = Zr, Hf) have been obtained as polycrystalline powders giving X-ray diffraction patterns characteristic of defect cubic pyrochlores, space group
(No. 227), Z = 8. The best discrepancy R factors, from 0.0265 for Rb(Ti0.5Te1.5)O6 to 0.0554 for Cs(Zr0.5W1.5)O6, were obtained for the B cations randomly distributed at 16(d), A ions at one quarter of 32(e), and oxygen atoms at 48(f) positions. A linear relationship is observed between the a unit cell parameters and the ionic radii of the A cations, as well as the average ionic radii of the B atoms. The results of electrical resistivity measurements for A(Ti0.5Te1.5)O6 (A = K, Rb, Cs, Tl) are given. 相似文献
102.
本文提出从高分辨电子显微像中,利用光学、全息和部分相干等方法,提取传递函数,制作相位和振幅滤波器,实现解卷,提高高分辨电子显微像的分辨率. 相似文献
103.
J.J. Pan Xiangdong Qiu Kejian Guan Liang Dong FengQing Zhou Wei Wang Mingjie Zhang James Guo Jun Yang Chunmeng Wu 《光学学报》2003,23(Z1)
A low cost, coolerless 980nm diode pumped, gain flattened L band EDFA with fast transient control, high pump efficiency and gain clamping effect was realized by using FBGs as C band seed generators. 相似文献
104.
105.
106.
Mechatronic subsystems have been extensively developed in automotive applications as they increase performance compared to passive components. The Hydractive CRONE suspension based on fractional differentiation is presented as a hybrid system undergoing an infinite sequence of autonomous switchings. The modelling and operation of Hydractive CRONE suspension as a hybrid system are presented. The stability of Hydractive CRONE suspension is demonstrated using the maximum principle extended to hybrid systems. Finally, comfort mode synthesis is proposed using the third generation CRONE control system design. 相似文献
107.
V. V. Popov T. V. Teperik O. V. Polischuk X. G. Peralta S. J. Allen N. J. M. Horing M. C. Wanke 《Physics of the Solid State》2004,46(1):153-156
The terahertz absorption spectra of plasmon modes in a grid-gated double-quantum-well field-effect transistor structure is analyzed theoretically and numerically using the scattering matrix approach and is shown to faithfully reproduce strong resonant features of recent experimental observations of terahertz photo-conductivity in such a structure. 相似文献
108.
X. H. Li Y. Z. Meng S. J. Wang A. Varada Rajulu S. C. Tjong 《Journal of Polymer Science.Polymer Physics》2004,42(4):666-675
The composites of biodegradable poly(propylene carbonate) (PPC) reinforced with short Hildegardia populifolia natural fiber were prepared by melt mixing followed by compression molding. The mechanical properties, thermal properties, and morphologies of the composites were studied via static and dynamic mechanical measurements, thermogravimetric analysis, and scanning electron microscopy (SEM) techniques, respectively. Static tensile tests showed that the stiffness and tensile strength of the composites increased with an increasing fiber content. However, the elongation at break and the energy to break decreased dramatically with the addition of short fiber. The relationship between the experimental results and the compatibility or interaction between the PPC matrix and fiber was correlated. SEM observations indicated good interfacial contact between the short fiber and PPC matrix. Thermogravimetric analysis revealed that the introduction of short Hildegardia populifolia fiber led to a slightly improved thermooxidative stability of PPC. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 666–675, 2004 相似文献
109.
A new method for the synthesis of exfoliated graphite and polyaniline (PANI)/graphite nanocomposites was developed. Exfoliated graphite nanosheets were prepared through the microwave irradiation and sonication of synthesized expandable graphite. The nanocomposites were fabricated via the in situ polymerization of the monomer at the presence of graphite nanosheets. The as-synthesized graphite nanosheets and PANI/graphite nanocomposite materials were characterized with Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis (TGA). The conductivity of the PANI/graphite nanocomposites was dramatically increased over that of pure PANI. TGA indicated that the incorporation of graphite greatly improved the thermal stability of PANI. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1972–1978, 2004 相似文献
110.
Qingbiao Yang Zhenyu Li Youliang Hong Yiyang Zhao Shilun Qiu Ce Wang Yen Wei 《Journal of Polymer Science.Polymer Physics》2004,42(20):3721-3726
Although there have been many reports on the preparation and applications of various polymer nanofibers with the electrospinning technique, the understanding of synthetic parameters in electrospinning remains limited. In this article, we investigate experimentally the influence of solvents on the morphology of the poly(vinyl pyrrolidone) (PVP) micro/nanofibers prepared by electrospinning PVP solution in different solvents, including ethanol, dichloromethane (MC) and N,N‐dimethylformamide (DMF). Using 4 wt % PVP solutions, the PVP fibers prepared from MC and DMF solvents had a shape like a bead‐on‐a‐string. In contrast, smooth PVP nanofibers were obtained with ethanol as a solvent although the size distribution of the fibers was somewhat broadened. In an effort to prepare PVP nanofibers with small diameters and narrow size distributions, we developed a strategy of using mixed solvents. The experimental results showed that when the ratio of DMF to ethanol was 50:50 (w/w), regular cylindrical PVP nanofibers with a diameter of 20 nm were successfully prepared. The formation of these thinnest nanofibers could be attributed to the combined effects of ethanol and DMF solvents that optimize the solution viscosity and charge density of the polymer jet. In addition, an interesting helical‐shaped fiber was obtained from 20 wt % PVP solution in a 50:50 (w/w) mixed ethanol/DMF solvent. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3721–3726, 2004 相似文献